Some seafood has to be heavily salted, i.e., needs to be thermally processed in a 4 to 5% brine, in order to retain an acceptable texture. By "thermal processing" is meant the seafood has been subjected to a time/temperature parameter which results in a "commercially sterilized" food, as defined in Title 21 CFR Part 113 (Definitions, Sec. 113.3) "Commercial sterility of thermally processed food means the condition achieved--
"(i) By the application of heat which renders the food free of-- PA0 "(ii) By the control of water activity and the application of heat, which render the food free of microorganisms capable of reproducing in the food under normal nonrefrigerated conditions of storage and distribution."
"(a) Microorganisms capable of reproducing in the food under normal nonrefrigerated conditions of storage and distribution; and PA1 "(b) Viable microorganisms (including spores) of public health significance; or
Texture herein generically refers to firmness in relation to touch and bite, and to material consistency and physical integrity. According to the present state of the art, if salt is not used, there is a loss of texture during thermal processing resulting in lack of firmness and resistance to one's bite, which is deemed unacceptable by many people.
From the moment of the death of the seafood item, e.g., the shrimp, sardines, or salmon, there is a deterioration in texture due to enzymatic and bacterial action. The result is a breakdown of the connective tissue. Although enzymatic action is largely terminated by the blanching process, blanched shrimp are still extremely heat sensitive, and further loss of texture can occur due to the elevated temperatures involved in thermal processing. Conventionally, a heavy dosage of salt (4 to 5% in the brine) is added to help preserve the texture of the blanched shrimp which would otherwise be degraded during thermal processing.
Some seafoods such as shrimp are presently heavily salted both during the blanch and also in the brine immediately prior to thermal processing (usually 5% by weight sodium chloride in the brine) in order to retain the texture. The consumer ordinarily removes some salt from the shrimp by a water wash or leach before the product is served. Nonetheless, considerable salt is or may be retained in the shrimp in a quantity which many medical authorities consider inimical to health, notably inducement of hypertension due to sodium retention.
Protein foods such as seafood contain sulfur compounds which may break down to react with exposed metal to produce a dark discoloration found in cans of protein-containing foods. Although the dark sulfide compound formed is harmless to consumer health, it detracts from the appearance of the can and when transferred to the product detracts from the appearance of the product.
Scientific studies have shown that the amount of sulfide released from seafood during thermal processing can be related to the acidity of the product. Seafoods, and particularly shell fish, have a tendency toward rapid degradation prior to canning with resultant high pH. Good handling conditions such as prompt icing and rapid processing are very important since they affect pH level and sulfide formation. Acidification reduces the pH and the consequent likelihood of black iron sulfide formation. Citric acid is frequently added to the canning brine by shrimp canners in an attempt to inhibit sulfide build-up and consequent product discoloration, but treatment with citric acid does not always fully inhibit build-up. This build-up is most likely to occur at exposed metal at the side seam of a three-piece metal can, at the countersink area, or on the profile rings of the container end.
One of the objects of the present invention is to produce canned seafood, for example, shrimp, which compares favorably with the fresh or frozen product which is not thermally processed. Another object is to retain the texture of seafood, for example, during thermal processing and storage by a treatment other than heavy salting, by combining an acid and its lactones, preferably an aldonic acid and its lactones, with the shrimp, to be processed with little or no salt added, thereby retaining a flavor closer to that of the fresh product. Further objects of the invention are to avoid the need to soak salt from the product before consumption and to improve the flavor by this substantial reduction in salt level. An added advantage is the reduction in discoloration of the seafood and of the metal can in which the seafood may be packed. It is also an object of the present invention to effect the above objectives by thermally processing seafood, for example, shrimp, sardines, or salmon, in the presence of an aldonic acid, preferably gluconic acid, which replaces salt for retaining texture.
Still another object of the invention is to provide commercially sterilized shrimp which has a clean shrimp flavor and odor.
Practice of this invention eliminates the need for or the use of citric acid in brine to reduce black iron sulfide formation and consequent product discoloration. When an aldonic acid lactone such as glucono-delta lactone is hydrolyzed to gluconic acid, the gluconic acid can perform the same inhibiting action as citric acid. Thus, when GDL is used alone in the brine, neither salt nor citric acid needs to be included since the gluconic acid formed from hydrolysis of the GDL performs these texturing and inhibiting functions.